1. Field of The Invention
This invention relates to a magnetic disc apparatus and a method of recording and reproducing information in the magnetic disc apparatus, and more particularly to a magnetic disc apparatus suitable for use as an external storage of a host device such as computer, to a thin film magnetic head for use in that magnetic disc apparatus and to a method for recording/reproduction of information in that magnetic disc apparatus.
2. Description of The Prior Art
Concomitantly with an increase in the storage capacity of the magnetic disc apparatus, the track density of the magnetic disc tends to increase more and more.
Therefore, the dimension of the track width of the magnetic pole tip of the thin film magnetic head mounted to the magnetic disc apparatus is decreased more and more.
In the thin film magnetic head, upper and lower magnetic cores form a magnetic circuit having a gap at their tips confronting the magnetic disc with an insulating film of a non-magnetic material interposed therebetween.
The magnetic circuit is activated to permit writing or reading a recording medium exemplified as the magnetic disc
The magnetized state of the recording medium which governs the recording density is affected by the magnitude of a magnetic field generated in the magnetic gap region.
The configuration of the upper and lower magnetic pole tips of the thin film magnetic head confronting the magnetic disc is one of the main factors for determining the recording density of the magnetic disc apparatus.
The configuration of the magnetic pole tip confronting the magnetic disc has hitherto been studied from various viewpoints.
The difference in width between the upper and lower magnetic pole tips has not been noticed frequently but is particularly referred to in U.S. Pat. No. 4,219,855 and in SHINGAKU GIHO, Vol. 85, No. 137, MR85-22 (1985). The term "width" of the magnetic pole tip indicates a lateral dimension of the pole tip face to be faced to the recording medium when recording or reproducing as measured in a direction perpendicular to the direction of movement of the magnetic head relative to the recording medium.
U.S. Pat. No. 4,219,855 describes that by making the width of the upper magnetic core tip smaller than that of the lower magnetic pole tip, an undesirable contour called a wraparound due to non-uniformity in manufacture can be avoided.
In SHINGAKU GIHO, Vol. 85, No. 137, MR85-22 (1985), computer simulation is used to study the relation of the difference in width between the upper and lower magnetic pole tips to the magnitude of a magnetic field at fringes of both sides of the magnetic pole tips. The term "magnetic fringe field" or "fringe flux" is used in this specification to indicate a part of the magnetic field or flux produced by a magnetic head at fringes slightly exceeding the width of the magnetic pole tip.
The latter literature describes that the magnetic fringe field adversely affects write/read characteristics and therefore the difference in width between the upper and lower magnetic pole tips should desirably be zero. The fringe field is also disclosed in "Magneto-optic Determination of Magnetic Recording Head Fields" by Mark E. Re et al. in IEEE Transaction on Magnetics. Vol. MAG. 22, No. 5, September 1986.
The prior art described in the aforementioned U.S. Pat. No. 4,219,855 fails to refer to how much the prescribed difference in width between the upper and lower magnetic pole tips should be in order to obtain a magnetic field distribution suitable for increasing the recording density.
Also, the prior art described in the aforementioned SHINGAKU GIHO, Vol. 85, No. 137, MR85-22 (1985) in no way points out that as the track width decreases, the magnetic fringe field rather improves write/read characteristics.
Further, neither of these two references gives the knowledge of the optimum relation between the track density of the magnetic disc and the difference in width between the upper and lower magnetic pole tips which is optimized for increasing the recording density of the magnetic disc apparatus.